1. Field of the Invention
The present invention relates to laminated safety glass of the type found in vehicles (e.g., windshields) and in architectural applications (e.g., windows and doors). More particularly, the present invention relates to laminated safety glass wherein a polyvinyl acetal sheet is laminated to at least one sheet of glass.
2. Description of the Prior Art
Laminated safety glass prepared by laminating a thermoplastic interlayer between two sheets of glass is well known in the prior art. Such laminates are widely used in automobile windshields and as windows and doors in architectural applications.
In recent years there has been a growing interest in laminated safety glass wherein only one sheet of glass is used, usually on the outboard side, that is, the side of the laminate that faces the outside of the vehicle or architectural structure. The inboard glass sheet, that is, the glass sheet that faces the interior of the vehicle or the architectural structure, is not used. The result is a glass/plastic laminate which is sometimes referred to as a bilayer or a bimodal laminate. The plastic component of the bilayer may be a single sheet or a composite of two or more components. These include a plastic component which is coated with another material, two or more plastic components laminated together, and various combinations of the above. Examples of such bilayer or bimodal construction are taught in U.S. Pat. Nos. 3,625,792, 3,652,379, 3,762,981, 3,781,184, 3,806,387 and Belgium Pat. No. 803,902.
Bilayer or bimodal laminated safety glass constructions have received widespread interest because of the theory that a person who collided with the laminate from the inboard side would tend to suffer less serious injuries by hitting a plastic component rather than a glass component. However, the dropping of the inboard glass sheet in laminated safety glass has given rise to new problems. The thermoplastic interlayer, which is no longer encased by the protective glass components, is now more susceptible to degradation which may adversely affect the properties of the laminate. Moreover, plastic sheets which are plasticized in order to obtain optimum physical properties may suffer from loss of plasticizer and a deterioration of properties. It has been proposed in the prior art to cover the plastic sheet with a protective coating or a protective layer. Many of the suggested coverings or coatings do not provide the desired level of protection to the plastic sheet.
Thus, a need exists in the art for a bilayer laminated safety glass wherein the plastic sheet, which is in laminated contact with the glass sheet, is stabilized against resin degradation.